Forbes— Igneous Rocks of Staffordshire, 25 



their present appearance, were in reality one and the same rock, or, 

 rather, were originally identical, and in all probability erupted from 

 one focus, and were more or less contemporaneous. 



He could not, however, endorse the opinion, that they were 

 contemporaneous with the Coal-measures, but was rather inclined 

 to look upon them as of later date, intruded after the consolida- 

 tion of the coal. For this reason also he was disposed to look 

 upon the belt of what was termed basaltic ash, as laid down in the 

 latest edition of the maps of the Ordnance Geological Survey, as 

 rocks decomposed in situ — in part consisting of decomposed igneous 

 rock, and in part of the decomposed previously altered sedimentary- 

 rocks in contact with the same ; believing that the present Eowley 

 Hills had been exposed and laid bare, by denudation of the strata 

 which he supposed to have originally covered them when they were 

 an irregular mass of igneous rocks imbedded in the strata, similar to 

 what could be seen at Pouk Hill. The apparent height of the 

 Eowley Hills, if looking upon them as a mass of igneous rock, 

 as they until lately had generally been regarded, was quite decep- 

 tive ; the recent sinkings and cuttings having demonstrated that the 

 igneous rock is but a superficial cap, at most of inconsiderable 

 depth. The Netherton canal tunnel, which was driven through the 

 very base of the Eowley Hills from one side to the other, showed 

 that this cap of igneous rock had been erupted through a dyke 

 not more than eight feet wide, and which was the only one cut 

 through in driving the entire length of the tunnel, and which 

 was apparently the only channel or conduit. The terms of basalt, 

 greenstone, trap, white rock trap, feldspathic rock, and locally, 

 Eowley Eag, white horse, green rock, etc., had all been applied to 

 these igneous rocks, without much discrimination, and it was to be 

 regretted that in England much looseness prevailed in the nomen- 

 clature of the Plutonic rocks. A microscopic examination of the 

 close grained and more compact varieties effected completely that 

 which the naked eye could do in the case of the more crystalline and 

 coarser grained rocks, and showed them in every case to be com- 

 posed chiefly of soda, lime, and feldspar (possibly labradorite) , along 

 with a small amount of augite and a small amount of titano-ferrite 

 or titanite of iron, which was never wanting. Other minerals were 

 but seldom present, but traces of zeolites and carbonate of lime 

 might occasionally be found, and possibly a little olivine, though its 

 existence was not yet satisfactorily proved. The rock was there- 

 fore what might be termed a true Dolerite, which must consequently 

 be regarded as the sole igneous rock of the district. The presence 

 of titanium was peculiarly constant where these rocks were found. 



However altered and decomposed they might appear, as in the 

 white rock or in the red clay, on the slopes of the Eowley Hills, 

 proceeding from the disintegration of the igneous rock itself — there 

 was found the titanium, which thixs furnished an excellent guide for 

 tracing out the connection with the parent mass. He had made 



